As used herein, the term “local” includes the part of the Data Communication Network (DCN) hierarchically below the Gateway NEs, whilst the term “external” includes the part of the DCN hierarchically above the Gateway NEs.
As used herein, the term “management system” includes the Network Management System (NMS) and the Element Management System (EMS).
A typical Data Communication Network (DCN) consists of Network Elements (NEs) interconnected to an external DCN via an Ethernet Interface (Gateway NE), the NEs being at a lower hierarchical level than the Gateway NEs. The NEs may be connected via embedded channels inside the traffic lines such as Synchronous Transmission Module-n (STM-n) for Synchronous Digital Hierarchy (SDH) or optical channels for Dense Wavelength Divisional Multiplexing (DWDM). These embedded channels are called, depending from the kind of frame overhead they use, Data Communications Channels (DCCs), Optical Supervisory Channels (OSCs), General Communications Channels (GCCs), and others. To realise an end to end connection between the Operational Support System (OSS) applications and managed NEs, an out of band DCN component is additionally deployed as based on dedicated high performance routers interconnected by high-bandwidth links.
Those skilled on the art will appreciate that the Open System Interconnection (OSI) reference model divides communication within the DCN into seven layers. It should be noted, however, that the OSI Reference Model is simply a guideline and that actual protocol stacks may combine one or more of the OSI layers into a single layer. The present invention is primarily concerned with Layer 3 in the OSI classification, namely the Network Layer. This layer determines the way in which data is sent to the recipient device and includes logical protocols, routing and addressing.
In particular, the present invention concerns the Internet Protocol (IP), which is a Layer 3 protocol. It will be appreciated that the Layer 3 Protocol Data Unit (PDU) is known in the art as a “packet” or a “datagram”, and may contain user data and/or control information such as address information. Within the IP protocol, each NE, Gateway NE etc is identified by a unique IP address. As used herein, the term “node” applies to any device with an IP address.
Each packet contains the IP address of the sender and intended recipient(s). The IP protocol transmits packets between intermediate nodes using IP routers, which determine the optimum path for transmission of the packet to the recipient.
In general, an IP DCN normally operates a dynamic routing protocol to find alternate routes whenever a link becomes unavailable. As part of dynamic routing, the packets are transmitted through the internetwork one hop at a time; each intermediate destination is calculated by matching the address of the intended recipient (as encoded within the packet) with the current node's routing table. As such, each node simply forwards a packet to its next destination and does not monitor whether the packet reaches its intended recipient. This is known as a “Best Effort” service since it does not provide full reliability.
To support specific business requirements, the Internet Engineering Task Force (IETF) acknowledged the need for a method of providing differentiated classes of service for Internet traffic. The Differentiated Services Working Group of the IETF defined the Differentiated Services (DiffServ or DS) model. DiffServ operates on the principle of traffic classification: each packet is assigned a 6-bit Differentiated Services Code Point (DSCP) field for packet classification purposes. The DSCP value of a packet determines the priority that is assigned to it as it is routed through the internetwork. It will be appreciated that it is generally desirable to prioritise management traffic over other IP traffic flowing through the DCN.
For local in-band communications of known DCNs, the NEs usually allocate dedicated routing resources to manage traffic flowing through the DCN channels. Accordingly, management traffic is not expected to compete with IP traffic related to other applications, and thus local IP management traffic is assigned a DSCP value corresponding to a basic priority. However, given the need to route an increasing volume of management traffic through the DCN channels, it is anticipated that the current situation will become problematic. In particular, it is anticipated that, due to the limited capacity of the dedicated routing resources, a relatively small increase in the total volume of traffic will force the management traffic to compete with IP traffic related to other applications.
When the management traffic reaches a Gateway NE, it passes from the local part of the DCN to the external part thereof. It will be appreciated that in this transition, the traffic passes from Layer 3 to Layer 2 within the OSI classification. During the transition from Layer 3 to Layer 2, the DSCP value of a Protocol Data Unit (“packet” in Layer 3) is mapped to a Class of Service (CoS) value using CoS translation tables configured on the Gateway NE. CoS operates at Layer 2 whilst DCSP operates at Layer 3, but both fields serve to indicate the level of priority is assigned to the Protocol Data Unit. It will be appreciated that the Gateway NE may assign management traffic a higher priority than traffic related to other applications during translation from DSCP to CoS.
As noted above, the present system is likely to become inadequate if the volume of management traffic were to increase. It is therefore desirable to prioritise management traffic against other routed traffic, and particularly for prioritising management traffic within the Internet Protocol, which operates in Layer 3.